Various waveguide grating structures have already been described in the PCT applications PCT/EP94/02361 and PCT/CH98/00389. The beam guiding, however, is not optimal. The reflected beam of a first incident light wave coincides with the direction of a second incident light wave. The reflected light beam and the second incident light beam oppositely have the same direction, which may lead to perturbations. The PCT applications PCT/EP94/02361 and PCT/CH98/00389 do not illustrate how a waveguide grating sensor structure that consists of two-dimensionally arranged sensor locations may be read out in parallel in the case of detection free of marking. Parallel reading-out is, however, necessary in order to achieve a higher throughput.
In the European patent application EP 0 482 377 A2 the waveguide grating is illuminated with a focussing light field. A focussing light field is not suitable for simultaneous illumination of a two-dimensional array of waveguide grating sensors. Furthermore, there is no mention of a method for temperature compensation in this application.
In Sensors and Actuators B 38-39 (1997), 116-121, a sensor location and a reference location of the waveguide grating are illuminated using the multiplex method. Also there is shown no one-dimensional or two-dimensional beam expansion of the incident light beam.